Retroreflective sheetings, which retroreflect a light incident thereon, towards the light source, have heretofore been well known and, for their retroreflecting property, have been widely used in the above-mentioned application fields.
These conventional retroreflective sheetings, however, have various problems when used particularly in cold districts. For example, when the atmospheric temperature falls below 0.degree. C., the waterdrops adhering on the surface of retroreflective sheeting freeze, resulting in reduced retroreflecting property of the sheeting; and, when there is snowfall, snow adheres on the surface of retroreflective sheeting and, in an extreme case, the retroreflective sheeting may completely lose the display function of sign. Thus, there have often occurred, in cold districts, troubles such as reduction in visibility or retroreflecting property of retroreflective sheeting, caused by ice, snow or the like.
Various attempts have heretofore been made for prevention of the above-mentioned freezing or snow sticking of retroreflective sheeting in cold districts. For example, U.S. Pat. No. 5,087,508 discloses a method of fitting, to a sign, a heat-storing substance to prevent the freezing or snow sticking of the sign by utilization of the heat stored in the substance. This method, however, has such problems as the fitting of the heat-storing substance to a sign is troublesome and needs an additional cost. Therefore, the method is very difficult to put into wide practical application.
Recently, in addition, there have occurred troubles (problems) that the surfaces of, in particular, signs such as road signs and construction signs are stained, by mischief, with a paint, an ink or the like, resulting in reduced display function of sign. Attempts have heretofore been made as well for recovery of the lost function of sign by removing the stain from the stained sign. For example, a method is in use which comprises coating, on the surface of a retroreflective sheeting, a solution of an acrylic crosslinking resin or the like, drying the resulting sheeting to form a solvent-resistant surface layer on the sheeting and, when the resulting sheeting is stained, wiping and removing the stain with an organic solvent. This method, however, has problems in that, in stain removal, a solvent capable of dissolving the stain must be used and this has adverse effects on operator's health and operational environment.
Furthermore, there is also known a so-called enclosed lens retroreflective sheeting obtained by using a fluorine-contained resin film as at least part of a retroreflective sheeting. For example, there is disclosed, in the gazette of Japanese Patent Application Laid-Open No. 86701/1992, a retroreflective sheeting of ultrahigh weatherability comprised of a surface layer made of a fluorine-contained resin film, laminating thereon a substantially mono-layer of glass beads of high refractive index and a focusing layer film in this order, and forming a metal layer on the focusing layer film.
According to the gazette, the above retroreflective sheeting of ultrahigh weatherability is produced by coating, on an appropriate supporting film, a coating composed mainly of a fluorine-contained resin solution, drying the resulting material to form a fluorine-contained resin surface layer, coating, on the surface layer, a coating to become a binder layer film, drying the resulting material to form a binder layer film, embedding glass beads in the binder layer film, coating thereon a coating to become a focusing layer film, drying the resulting material to form a focusing layer film, and forming a metal reflecting layer on the focusing layer film. It is also disclosed in the gazette that an intermediate layer may be formed between the surface layer and the binder layer in a similar manner.
However, many of low-surface tension resins such as fluorine-contained resin and the like have low solubility in organic solvents. In preparation of an organic solvent solution of such a resin, there are problems, for example, in that the range of selectable resins is narrow and care is needed in selection of organic solvent used. Thus, no truly satisfactory retroreflective sheeting is obtained at present.
The object of the present invention is to provide a retroreflective sheeting which is improved by simple operation so that the sheeting is endowed with freezing resistance and resistance to snow sticking and further that, even when the surface of an article (e.g. a sign) using the retroreflective sheeting is stained with a paint, an ink or the like, the stain can be easily removed only by wiping with dry cloth or water washing, without using any wiping solvent which gives adverse effects to human body or environment.